High amounts of THD over USB and Coax...

[tboooe]

dumb question...are these results the same if you use different players like Volumio? It shouldnt make a difference but you never know. Also, in Rune did you change any of the sound settings? What about volume normalization and replay gain? All off?

[PeteB]

Hard to be certain without seeing it at a higher time resolution, but the recorded signal looks clipped like a filtered line input being overdriven (not compressed).

What is the peak-to-peak voltage of the signal, compared to the maximum voltage range of the input on the PC where the RMAA software is running?

The analog output of the Pi, and the analog output of a standalone DAC are not necessarily the same voltage. Even if they did reproduce the signal exactly the same, the absolute gain would be different, unless it is adjusted.

If the higher peaks of the DAC output come close to or exceed the max line input of the ADC, you get some distortion, a little or a lot, depending on the conditions.

[robertzombie]

[robertzombie]

[PeteB]

Can you just decrease the amplitude(volume) anywhere along the path, record the signal, and see if it still looks clipped(compressed)? You may not want to do that for an actual test, but it will quickly show you if that is the problem.

edit:

In other words, if the input and output look the same at a lower volume, you know what the problem is, and then you can go about fixing it.

[robertzombie]

[PeteB]

I believe you, but I thought the same thing, and I turned out to be wrong. The software on a PC does not treat the USB connection to a DAC the same way as the software on the Pi. So, unless you can volume match the two...

What I see in your recorded signal is the higher volume sections being clipped... somewhere... not sure where. My next step, I would cut the volume 50% (-6db) and record it again. However, it is your test, so you should def do it your way... just like I would!

(looks like you are close to the solution either way)

Best,

Pete

[robertzombie]

[robertzombie]

Finally getting somewhere! Results to follow...

[robertzombie]